Along with improvement in the degree of integration and in the processing capacity of an integrated circuit, the amount of data exchanged between a plurality of integrated circuits is increasing, and thus, it is desirable that the data rate increases. The data rate can be increased by transmitting data in parallel, which, however, raises the cost because the number of terminals of an integrated circuit increases, and makes skew adjustment between data difficult. In recent years, therefore, a high-speed serial transmission method is often adopted.